Problem: Let $S$ be a region in the plane with area 4.  When we apply the matrix
\[\begin{pmatrix} 2 & -1 \\ 7 & 2 \end{pmatrix}\]to $S,$ we obtain the region $S'.$  Find the area of $S'.$
Explanation: Note that
\[\begin{vmatrix} 2 & -1 \\ 7 & 2 \end{vmatrix} = (2)(2) - (-1)(7) = 11,\]so the matrix scales the area of any region by a factor of 11.  In particular, the area of $S'$ is $11 \cdot 4 = \boxed{44}.$